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The Medium-Deep Survey (MDS) is a Key Project for the Hubble Space Telescope (HST) which is allocated 200 hours/year for parallel mode observations using the Wide Field Camera (WFC), when another HST detector is used for observing a primary target. The MDS data base is comprised of randomly distributed fields observed with single or multi-orbit HST V- and I-band exposures, with exposure times 1200--2400s. Using the HST's high-resolution and low sky background, these images can be used to study the morphology of galaxies at flux levels too faint to study from the ground.
For extracting galaxy positions from WFC images the detection threshold must be well-defined and applied uniformly to avoid field-to-field differences arising from the search method applied to each frame. We examine a space of parameters for optimizing the detection of faint galaxies found in WFC images by the Faint Object Classification and Analysis System (FOCAS). We consider the effects of convolving and/or rebinning of WFC images for improving the detection efficiency. Catalog reliability and completeness and errors in photometry and positions are presented for galaxy images with disk and bulge profiles, as observed with WF/PC-1 and WFPC2 for a wide range of apparent magnitudes and scale lengths.
